The present invention relates to semiconductor devices, and more particularly to devices for use in mounting semiconductor devices to a submount in a flip-chip configuration.
GaN-based light emitting diodes (LEDs) typically comprise an insulating or semiconducting substrate such as SIC or sapphire on which a plurality of GaN-based epitaxial layers are deposited. The epitaxial layers comprise an active region having a p-n junction that emits light when energized. A typical LED is mounted substrate side down onto a submount, also called a package or lead frame (hereinafter referred to as a xe2x80x9csubmountxe2x80x9d). FIG. 1 schematically illustrates a conventional LED having an n-type SiC substrate 10, an active region 12 comprising an n-GaN-based layer 14 and a p-GaN-based layer 16 grown on the substrate and patterned into a mesa. A metal p-electrode 18 is deposited on the p-GaN layer 16 and a wire bond connection 28 is made to a bond pad 20 on the p-electrode 18. An n-electrode 22 on the conductive substrate is attached to metallic submount 24 using a conductive epoxy 26. In the conventional process, the conductive epoxy 26 (usually silver epoxy) is deposited on the submount and the LED is pressed into the epoxy 26. The epoxy is then heat cured which causes it to harden, providing a stable and electrically conductive mount for the LED chip. Light generated in the active region 12 is directed up and out of the device. However, a substantial amount of the generated light may be transmitted into the substrate and absorbed by the epoxy 26.
Flip-chip mounting of LEDs involves mounting the LED onto the submount substrate side up. Light is then extracted and emitted through the transparent substrate. Flip chip mounting may be an especially desirable technique for mounting SiC-based LEDs. Since SiC has a higher index of refraction than GaN, light generated in the active region does not internally reflect (i.e. reflect back into the GaN-based layers) at the GaN/SiC interface. Flip chip mounting of SiC-based LEDs may improve the effect of certain chip-shaping techniques known in the art. Flip chip packaging of SiC LEDs may have other benefits as well, such as improved heat dissipation, which may be desirable depending on the particular application for the chip.
One problem with flip-chip mounting is illustrated in FIG. 2. Namely, when a chip is flip-chip mounted on a conductive submount or package using conventional techniques, a conductive die attach material 26 is deposited on the chip and/or on the submount 24, and the chip is pressed into the submount 24. This can cause the viscous conductive die attach material 26 to squeeze out and make contact with the n-type layers 14 and 10 in the device, thereby forming a Schottky diode connection that short-circuits the p-n junction in the active region with predictably undesirable results. Thus, improvements in the flip-chip mounting of LEDs may be desirable.
Embodiments of the present invention provide for bonding of flip-chip mounted light emitting devices having an irregular configuration. Certain embodiments of the present invention bond a light emitting diode having a shaped substrate to a submount by applying forces to the substrate in a manner such that shear forces within the substrate do not exceed a failure threshold of the substrate. Such bonding may, for example, be provided by thermosonic and/or thermocompression bonding. In certain embodiments of the present invention, a light emitting diode is bonded to a submount is by applying force to a surface of a substrate of the light emitting diode that is oblique to a direction of motion of the light emitting diode to bond the light emitting diode to the submount.
In particular embodiments of the present invention, force is applied to the shaped substrate by mating a collet to the surface of the substrate oblique to the direction of motion and moving the collet in the direction of motion. Such a mating of the collet may be provided by seating a collet having a mating surface corresponding to an oblique surface of the substrate so that the mating surface of the collet contacts the oblique surface of the substrate. In certain embodiments of the present invention, the mating surface of the collet is a fixed surface relative to a body of the collet. In other embodiments of the present invention, the mating surface of the collet is a moveable surface relative to a body of the collet.
In still further embodiments of the present invention the collet is seated by placing the collet over the light emitting diode and applying a vacuum pressure to the collet. In certain embodiments of the present invention, the light emitting diode is a gallium nitride based light emitting diode having a silicon carbide shaped substrate. In particular, the silicon carbide shaped substrate may have a cubic portion and a truncated pyramidal portion adjacent the cubic portion. In such cases, force is applied to sidewalls of the truncated pyramidal portion of the silicon carbide substrate.
In additional embodiments of the present invention, a collet for bonding light emitting diodes having a shaped substrate to a submount is provided. The collet has a body having a chamber therein and an opening in communication with the chamber and adapted to receive the light emitting diode. The collet also includes means for mating surfaces of the collet to surfaces of the shaped substrate that are oblique to a direction of motion of the collet.
In certain embodiments of the present invention, the means for mating surfaces of the collet to the shaped substrate is provided by fixed surfaces of the collet defining the opening and disposed at an angle corresponding to an angle of the surfaces of the shaped substrate that are oblique to the direction of motion. Furthermore, the body may include a top portion and vertical side portions defining the chamber and an opening for inducing a vacuum in the chamber.
In further embodiments of the present invention, the body includes spaced apart side portions defining the chamber. In such embodiments, the fixed surfaces of the collet may be provided by angled surfaces at a terminus of the side portions. Furthermore, the side portions may be spaced apart a distance corresponding to a dimension of the surfaces of the shaped substrate that are oblique to the direction of motion. In such embodiments, the body may also include a top portion and an opening for inducing a vacuum pressure in the chamber. The side portions may then be vertical side portions.
In still further embodiments of the present invention, the body includes a top portion and vertical side portions defining the chamber and an opening for inducing a vacuum in the chamber. In such embodiments, the side portions may be horizontal side portions that extend from the vertical side portions and are spaced apart from the top portion.
In additional embodiments of the present invention, the means for mating surfaces of the collet to the shaped substrate is provide by surfaces of the collet defining the opening and that are moveable with respect to the body and are configured to adjust to an angle corresponding to an angle of the surfaces of the shaped substrate that are oblique to the direction of motion. In such embodiments, the body may include a top portion and vertical side portions defining the chamber and an opening for inducing a vacuum in the chamber. Furthermore, the body may include spaced apart horizontal side portions. In such a case, the moveable surfaces of the collet may be provided by moveable end portions of the horizontal side portions, the moveable end portions being configured to substantially conform to the angle of the shaped substrate and are spaced apart a distance corresponding to a dimension of the surfaces of the shaped substrate that are oblique to the direction of motion.
In certain embodiments of the present invention, the moveable end portions are hinged to rotate about an end of the horizontal side portions. In further embodiments of the present invention, the body further includes a top portion and vertical side portions that connect the top portion to the horizontal side portions defining the chamber and an opening for inducing a vacuum pressure in the chamber. The horizontal side portions may also be moveably connected to the vertical side portions. For example, the horizontal side portions may be hinged to the vertical side portions.
In particular embodiments of the present invention, the collet is adapted for use with a gallium nitride based light emitting diode having a silicon carbide shaped substrate. The collet may also be adapted for use with a silicon carbide shaped substrate having a truncated pyramidal portion and wherein the means for mating comprises means for mating surfaces of the collet to sidewalls of the truncated pyramidal portion of the shaped silicon carbide substrate.
Still further embodiments of the present invention provide a collet for bonding a light emitting diode having a shaped substrate to a submount. The collet includes a body having a chamber therein and an opening in the body in communication with the chamber configured such that a portion of the shaped substrate extends into the chamber without contacting the body. The colet further includes means, operably associated with the chamber, for engaging the substrate to bond the light emitting diode to the submount while maintaining internal shear forces of the substrate below a shear failure threshold of the substrate.
In some embodiments of the present invention, the means for engaging is provided by fixed surfaces of the collet defining the opening and disposed at an angle corresponding to an angle of the surfaces of the shaped substrate that are oblique to the direction of motion. In such embodiments, the body may include a top portion and vertical side portions defining the chamber and an opening for inducing a vacuum in the chamber. In other embodiments, the body includes spaced apart side portions defining the opening and wherein the fixed surfaces of the collet comprise angled surfaces at a terminus of the side portions, wherein the side portions are spaced apart a distance corresponding to a dimension of the surfaces of the shaped substrate that are oblique to the direction of motion. In such embodiments, the body may also include a top portion defining the chamber and an opening for inducing a vacuum in the chamber and the side portions may be vertical side portions. In still other embodiments of the present invention, the body includes a top portion and vertical side portions and an opening for inducing a vacuum in the chamber and the side portions are horizontal side portions that extend from the vertical side portions and are spaced apart from the top portion.
In additional embodiments of the present invention, the means for engaging is provided by moveable surfaces of the collet defining the opening and configured to adjust to an angle corresponding to an angle of the surfaces of the shaped substrate that are oblique to the direction of motion. In such embodiments, the body may include a top portion and vertical side portions defining the chamber and an opening for inducing a vacuum in the chamber. The body may also include spaced apart horizontal side portions and wherein the moveable surfaces of the collet are moveable end portions of the horizontal side portions, the moveable end portions being configured to substantially conform to the angle of the shaped substrate and being spaced apart a distance corresponding to a dimension of the surfaces of the shaped substrate that are oblique to the direction of motion to thereby define the opening. In certain embodiments, the moveable end portions are hinged to rotate about an end of the horizontal side portions. In such embodiments, the body may also include a top portion and an opening for inducing a vacuum in the chamber and vertical side portions that connect the top portion to the horizontal side portions. Furthermore, the horizontal side portions may also be moveably connected to the vertical side portions. For example, the horizontal side portions may be hinged to the vertical side portions.
In still other embodiments of the present invention, a collet for bonding a light emitting diode to a submount is provided having a body having a chamber therein, an opening in the body in communication with the chamber and configured to receive the light emitting diode and fixed surfaces of the collet at the opening that contact a shaped substrate of the light emitting diode, the fixed surfaces defining the opening and being disposed at an angle corresponding to an angle of the surfaces of the shaped substrate that are oblique to a direction of motion of the collet during bonding. In some embodiments of the present invention, the body includes spaced apart side portions and the fixed surfaces of the collet may be angled surfaces at a terminus of the side portions. The side portions are spaced apart a distance corresponding to a dimension of the surfaces of the shaped substrate that are oblique to the direction of motion. In additional embodiments of the present invention, the body includes a top portion and vertical side portions defining the chamber and an opening for inducing a vacuum in the chamber. In such embodiments, the side portions may be horizontal side portions that extend from the vertical side portions and are spaced apart from the top portion.
In further embodiments of the present invention, a collet for bonding a light emitting diode to a submount includes a body having a chamber therein, an opening in the body in communication with the chamber and configured to receive the light emitting diode and moveable surfaces of the collet at the opening that are moveable in relation to the body and that contact a shaped substrate, the moveable surfaces being configured to adjust to an angle corresponding to an angle of the surfaces of the shaped substrate that are oblique to a direction of motion of the collet during bonding. In certain embodiments of the present invention, the body includes spaced apart horizontal side portions and the moveable surfaces of the collet are moveable end portions of the horizontal side portions, the moveable end portions being configured to substantially conform to the angle of the shaped substrate and are spaced apart a distance corresponding to a dimension of the surfaces of the shaped substrate that are oblique to the direction of motion. In some embodiments, the moveable end portions are hinged to rotate about an end of the horizontal side portions. In other embodiments of the present invention, the body includes a top portion defining the chamber, an opening for inducing a vacuum in the chamber and vertical side portions that connect the top portion to the horizontal side portions. In such embodiments, the horizontal side portions may be moveably connected to the vertical side portions. For example, the horizontal side portions may be hinged to the vertical side portions.
In still other embodiments of the present invention, a system for bonding a light emitting diode having a shaped substrate to a submount is provided. The system includes means for engaging the substrate while maintaining internal shear forces of the substrate below a shear failure threshold of the substrate when force is applied to the shaped substrate to bond the light emitting diode to the submount and means for moving the means for engaging to apply force to the substrate to bond the light emitting diode to the substrate. In certain embodiments of the present invention, the means for engaging comprises means for contacting the shaped substrate on a surface of the shaped substrate that is oblique to a direction of motion of the shaped substrate. In additional embodiments of the present invention, the means for contacting is provided by walls of a collet that are in a fixed position with respect to a body of the collet, the collet being configured to receive the light emitting diode. In other embodiments of the present invention, the means for contacting is provided by walls of the collet that are moveable with respect to a body of the collet, the collet being configured to receive the light emitting diode.
In further embodiments of the present invention, a collet for bonding light emitting diodes having a shaped substrate to a submount is provided. The collet includes a body having a chamber and an opening in communication with the chamber and adapted to receive the light emitting diode. The opening has a portion proximate to the chamber and a portion distal to the chamber. The collet also has mating surfaces associated with the, opening and disposed at an oblique angle with regard to an axis connecting distal portions of the opening that mate to surfaces of the shaped substrate.
In additional embodiment, the mating surfaces are fixed surfaces of the collet defining the opening and disposed at an angle corresponding to an angle of the surfaces of the shaped substrate. Furthermore, the body may have a top portion and vertical side portions defining the chamber and an opening for inducing a vacuum in the chamber. The body may be spaced apart side portions defining the chamber and the fixed surfaces of the collet may be angled surfaces at a terminus of the side portions. The side portions are spaced apart a distance corresponding to a dimension of the surfaces of the shaped substrate to which the fixed surfaces mate. The body may also include a top portion and an opening for inducing a vacuum pressure in the chamber and the side portions may be vertical side portions. The side portions may also include horizontal side portions that extend from the vertical side portions and are spaced apart from the top portion.
In other embodiments of the present invention, the mating surfaces are provided by surfaces of the collet defining the opening and that are moveable with respect to the body and are configured to adjust to an angle corresponding to an angle of the surfaces of the shaped substrate to which the surfaces of the collet defining the opening mate. The body may include a top portion and vertical side portions defining the chamber and an opening for inducing a vacuum in the chamber. The body may also include spaced apart horizontal side portions and the moveable surfaces of the collet may be moveable end portions of the horizontal side portions. The moveable end portions may be configured to substantially conform to the angle of the shaped substrate and may be spaced apart a distance corresponding to a dimension of the surfaces of the shaped substrate to which the moveable end portions mate. The moveable end portions may be hinged to rotate about an end of the horizontal side portions. The body may also include vertical side portions that connect the top portion to the horizontal side portions defining the chamber. The horizontal side portions may be moveably connected to the vertical side portions. For example, the horizontal side portions may be hinged to the vertical side portions.
In certain embodiments of the present invention, the collet is adapted for use with a gallium nitride based light emitting diode having a silicon carbide shaped substrate. The collet may also be adapted for use with a silicon carbide shaped substrate having a truncated pyramidal portion and wherein the mating surfaces mate with angled sidewalls of the truncated pyramidal portion of the shaped silicon carbide substrate.